add code to detect pure function currently do not unpin calls to const functions
add code to detect pure function
currently do not unpin calls to const functions

[r8012]

8l/libfirm,davidgiven/libfirm,libfirm/libfirm,davidgiven/libfirm,8l/libfirm,MatzeB/libfirm,killbug2004/libfirm,davidgiven/libfirm,jonashaag/libfirm,killbug2004/libfirm,MatzeB/libfirm,davidgiven/libfirm,killbug2004/libfirm,8l/libfirm,libfirm/libfirm,killbug2004/libfirm,8l/libfirm,jonashaag/libfirm,MatzeB/libfirm,8l/libfirm,jonashaag/libfirm,MatzeB/libfirm,davidgiven/libfirm,jonashaag/libfirm,MatzeB/libfirm,libfirm/libfirm,8l/libfirm,libfirm/libfirm,killbug2004/libfirm,davidgiven/libfirm,MatzeB/libfirm,libfirm/libfirm,killbug2004/libfirm,jonashaag/libfirm,jonashaag/libfirm,killbug2004/libfirm,jonashaag/libfirm,davidgiven/libfirm,8l/libfirm,MatzeB/libfirm